In an electric tool such an impact wrench that is driven by a commercial alternating current power supply, a universal motor (a series winding commutator motor) has been adopted as a driving source.
FIG. 8 illustrates an impact wrench as an electric tool using a universal motor. The impact wrench has a housing 1, a universal motor 10, a striking mechanism part 20 rotated by the universal motor, and an output part 30 connected to the striking mechanism part 20. The output part 30 is mounted with a variety of tip tools.
The housing 1 has a trunk part 2 accommodating therein the universal motor 10, the striking mechanism part 20 and a part of the output part 30, and a handle part 3 having one end connected to the trunk part 2. The handle part 3 is provided with a tumbler switch 4, and a power supply cord 5 is drawn out from a lower part of the handle part 3.
FIG. 9 is a circuit diagram showing an operation of switching stop, forward rotation and reverse rotation of the universal motor 10 by the tumbler switch 4. A field winding (a stator winding) 11 and an armature winding 12 of the universal motor 10 are connected in series to a commercial alternating current power supply 6 (for example, AC 100V) through contact points of two circuits of the tumbler switch 4. That is, the field winding 11 and the armature winding 12 are disconnected to stop the universal motor 10 when the tumbler switch 4 is at a neutral position, the field winding 11 and the armature winding 12 are connected in series with each other to forward rotate the universal motor 10 by operating the tumbler switch in a first direction, and a series connection relation between the field winding 11 and the armature winding 12 is switched to reversely rotate the universal motor 10 by operating the tumbler switch in a second direction. PTL 1 discloses an example of an alternating current-type electric tool, and PTL 2 discloses an example of a direct current-type electric tool.